Hand held low altitude bombsight



m m L AW H B E N mm m W W L D Rm 9 m1 4 1 w F d e l 1 F l a n i g i r 0 Dec. m, 1957 4 Sheets-Sheet l w. w m a T w MR Y 0B TARGET & ASPECT LIME 0F $/6HTM LEAD AMIGLE HORIZONTAL TRIANGLE s R O T N F- V m E N ESL WEAD-A RICHARD W. PITMAN FRA W. SGHLESINGER zfldflw ATTORNEY WET/GAL TRIANGLE Dec. 1%, 1&5? R. w. PITMAN ETAL HAND HELD LOW ALTITUDE BOMBSIGHT 4 Sheets-Sheet 2 Original Filed Feb. 14, 1951 mvsmoas RICHARD W. PITMAN FRAN W. Sfi'ILESINGE I, u BY ATTORNEY Dec. 10, 195? R. w. PITMAN EI'AL HAND HELD LOW ALTITUDE BOMBSIGHT Original Filed Feb. 14, 1951 4 Sheets-Sheet 3 mvararoas RICHARD W. PITMAN FRANK W. SGHLESINGER ATTORNEY Des. 1, 1957 R. w. PITMAN El'AL HAND HELD LOW ALTITUDE BOMBSIGHT ori inal Filed Feb. 14, 1951 4 Sheets-Sheet 4 INVENTORBI RICHARD w. PWMAN FRANKW. so

HESINGER qr mafia 2,815,694 HAND HELD LOW ALTITUDE BOMBSIGHT Richard W. Pitman, Philadelphia, Pa., and Frank W.

Schlesinger, Chicago, 111., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Original application February 14, 1951, Serial No. 210,968, now Patent No. 2,677,301, dated May 4, 1957. Divided and this application December 11, 1953, Serial No. 398,444

4 Claims. (Cl. 88-1) The present invention relates to bombsights and more particularly to a hand held bombsight for horizontal low altitude bombing especially adapted for antisubmarine combat. This application is a division of copending application, Serial No. 210,968, filed February 14, 1951, now U. S. Patent No. 2,677,301.

One object of the present invention is to provide aportable hand held bombsight which may be used in any airplane, and will indicate the proper instant for release of bombs for effective attack against stationary, moving and/or submerged targets when information concerning altitude, ground speed, target aspect and other pertinent data have been properly registered on the instruments controls.

Another object of this invention is to provide a portable bombsight which may be used to indicate accurately the optimum instant for release of the bombs even though the target, such as a submarine, submerges out of sight during the bombing run.

Still another object of the present invention is to provide a bombsight for stationary, moving, and/or submerged targets, which correlates three independent variables, airplane altitude and ground speed and the target aspect, to visually indicate the proper point for release of the bomb.

Still another object of the present invention is to provide a bombsight for stationary, moving, and/or submerged targets, which correlates the independent variables of airplane altitude and ground speed, a target aspect, and the characteristics of the bombs being used, to visually indicate the proper point for release of the bomb.

A still further object of the present invention is to provide an optical sighting system which presents an illuminated sighting image on a nonilluminated transparent sight plate, for facilitating proper sighting of targets under adverse light conditions.

Other objects will be apparent to those skilled in the art from the following detailed description of the present instrument made in conjunction with the accompanying drawings wherein:

Fig. 1 is a perspective View of the bombsight;

Figs. 2, 3 and 4 are diagrams depicting the various factors involved in accurate bombing, compensated for by the present invention;

Fig. 5 is a perspective view of the compensating apparatus of the bombsight, the casing being removed, and a partition wall partially cut away to reveal the entire apparatus;

Fig. 6 is a detailed view of the portion of the instrument wherein the representative horizontal triangle of the bombing factors are set up;

Fig. 7 is a face view of the operating surface of the altitude dial;

Fig. 8 is a cross-sectional view of the ground speed and bomb characteristic dial;

Fig. 9 is a detailed face view of the ground speed and bomb characteristic dial; and

Figs. 10 and 11 are views of the sight plate during a r bombing run on a surface target.

2,815,694 Patented Dec. 10, 1957 The general problems in bombing sidered, among which are the ground speed of the airplane, its elevation, the speed of the target if moving, air resistance, and the bomb characteristics. For high precision bombing other factors such as Wind velocity and wind direction also need be considered. But in the case of low altitude bombing these latter factors become negligible. The present bombsight, being designed particularly for low altitude bombing, is concerned, therefore, with the former factors and neglects the latter. In this section reference is bad to the diagrammatic representations of Figs. 2, 3, and 4.

In the 'case of a stationary target, neglecting wind velocity and direction and reserving consideration of air resistance and bomb characteristics for a subsequent discussion, one need consider only the airplanes velocity and altitude and theconstant acceleration of gravity. This situation is depicted in Fig. 3 wherein point G is the airplane, the line GR is the altitude of the airplane, and point C (or D) is the target. It is apparent that upon release of the bomb the velocity and direction of the airplane is im parted thereto forming one vector component of the bombs flight, while the downward force of gravity forms the other vector component. The resultant thereof is the trajectory of the bomb, while the range from the airplane to the target is represented by the solid line GC. Consequently, as the target is approached, the bombardier must determine at what point the bomb must be released, considering the above factors, for a hit to result. The present apparatus is designed to compensate for these factors and to indicate accurately the proper time for release of the bombs after the airplane ground velocity and altitude adjustments are made on the apparatus.

In the case of a moving target, the above factors must, of course, be considered, but in addition it becomes necessary to account for the direction and speed of the target. Neglecting the altitude and gravity components for the moment, reference to Fig. 2 illustrates the horizontal components. Line AB represents the direction of flight of the airplane while line SB represents the direction of movement of the target or the target aspect, angle ASE being the target aspect angle. When the plane is at some point R, before B, and is directed on a collision course with the target C, the bomb must be released, and following the course imparted to it by the course of the plane meets the target at B. Frequently, the only bearing that the bombardier may rely on is the target, and this is particularly true in antisubmarine warfare and marine bombing in general. Consequently, assuming a collision course, the bombardier must determine when to release the bomb from the range RC, the desired range being determined by the airplane altitude and ground velocity.

In actual practice, it is necessary to integrate all the factors above discussed to determine the proper point for release of the bomb. Fig. 4 is a three dimensional diagram combining the altitude diagram of Fig. 3, and a portion of the horizontal diagram of Fig. 2, to indicate the various factors involved in a bombing attack on a moving target. The bomb trajectory GC of Fig. 3 is, of course not applicable to this situation, but the trajectory here is indicated by the dotted line GB of Fig. 4. The variable components, the airplane altitude and ground velocity and the target aspect, the force of gravity being constant, are introduced into the bombsight and integrated therein, thereby enabling the bombardier to determine the proper point to release the bomb as indicated by the sight plate thereon Apparatus and operation The above is a general description of the several variable factors involved in bombing; the following is a detailed description of the apparatus of the present invention functioning to integrate the above-described variables set into the bombsight and providing an indicating means for determining the proper point for releasing the bomb. For the purposes of the'present' section the bomb eharacteristic variable is omitted and reserved for a later discussion.

The ground speed ofthe plane is introdiieedd rito the instrument by means o f the knurledg'r'oimdspeed dial having an indicia' bearingfiange iR o'tation ofithe ground speed dial to the desired setting translated into the instrument by means of the groundsp'eed pivot'arm 12, rotation of said dial causing a corresponding rotation ofgear 13 which in turn acts on rack 14 to raise or lower arm 12.

'When the airplane is on a collision;course"w ith the targetpthe target aspectfactor, see Fig; 2, is introduced by means of knurled target aspect angledial 15, which setting is indicated by the position of the target aspect arrow 16 on disc 17, the dial being linked to the disk 17 for corresponding rotation through gears 18 and 19. The correct target aspect setting is obtainedby sighting the target along the line of sight of the instrument, ,see Fig. 5, and turning knurled target aspect dial 15 until the target aspect arrow 16 points in the direction of the target course. The angle formed by the direction of the arrow with the line of sight is treated in the instrument as -the target aspect angle, although in error from the true target aspect angle by the amount of the lead angle, see Fig. 2, which, however, is generally very small. The target aspect setting is translated into the instrument by means of azimuth slide rack 20, which is mounted on dial 15 for rotation therewith and is slideable thereonalong elongated slots 21, said slidability being controlled by gear '22. For the present discussion, only the rotational movement of the rack is considered, the slideable movement'being reserved for a later discussion.

The center of chain guide ratchet 37 on pivot'arm 12, azimuth rack lug 24, and the center of azimuth gear22 form the azimuth rate triangle R'CB', shown in detail in Fig. 6, corresponding to the horizontal distance triangle RCB in Fig. 2, each side thereof being divided by the flight time from R to B to form the rate triangle. The side CB' represents the distance CB traveled by a target having a predetermined ground speed divided by said flight time, side 'R'B' the distance RB divided by said flight time, or the ground speed of the airplane, and side CR' the horizontal range between the airplane and the target divided by said flight time. Thus, the positioning of lug 24 so as to generate the angles BCR and C'BR by the setting of pointer 16, in error by the lead angle, to define the angle BR'C, makes the horizontal rate triangle RCB', this representative triangle depicting the ratios of the horizontal distance from the point of release of the bomb to the point of impact, to the distance from the target at the time of release of the bomb to the point of impact, to the horizontal range from the point of release of the bomb to the target at the time of release of the bomb as affected by the ground speed of the airplane and the course of the target, assuming the airplane is on a collision course with the target, and that the target is traveling at the predetermined speed for which the azimuth lug 24 is set.

As discussed in the previous section on the general problems of bombing, two triangles must be considered: the horizontal triangle considered above and the vertical triangle as defined by the airplane ground speed, its elevation, air resistance, and the force of gravity acting on the released bomb. In low altitude bombing the effect of wind velocity and direction on the trajectory of the falling bomb is negligible and may be ignored. Fig. 3 represents the vertical triangle, neglecting air resistance to be con sidered hereinbelow, letter G representing the airplane, line RG the altitude thereof, and letter C the target. As can readily be seen from the three dimensional representation of Fig. 4, when the target is traveling the course CB range CG meets thetarget at B.

To form the vertical trianglenecessary to complete the operation of the present bombsight, the altitude of the airplane is introduced through a knurled altitude dial 25 having an indicia bearing flange 26. This value is translated into the instrumenfbykheans of rocking arms 27 and 28 pivoting'abo'utj-rod 29 to slide leveling-bulb 30, its frame 31 having fiducial line or level zero indicator 32, and its associated"guide rod'133:reciprocably through bracket 10( The'rotation of dial 25 is translated into the rocking motion of arms 27 and 28 by means of pin 34 on rocking arm 27 engaging slot 35, the contour of said slot,

shown in'Fig. 7, being designed jto effectuate the desired and horizontal triangles. The values impressed'on C'R are transmitted to the-triangle CR-"G"*' by' means of chain 36. -Chain'36'is fixed'at one end' to rack lug 24, then passes around chain guidelug 23 onpivotarni 12 and around c og wheels 37, 38, 39 and 40 and is fixed at'itsother end to one-tine -ofthe bifurcated rod 41.

Another chain 42 works against helical spring 43 attached'at one-end to chain"42'?and*at-its' dther "end to fixed lug90. -'Chain""42 'hasone end fixedtoratchet' or cog'wheel"44 and is partially wound therearound. This ratchet" wheel=is fixed to ratchet'wheeh45 for uniform rotation therewith about pivot 46. 'A-third"'chain 47 is attached 'at oneend to ratchetwheeland is partially wound'therearo'und' andthen passesover "ratchet wheel furcated rod' 41. "Rod*'4lis fixed toslide block 101, slidably mou1ited in "slot 1023' and has the 'bracket' pivotally mounted on one end thereof for slidably carrying the leveling bulb guide" rod '33. Tlihs variations 'in C'R" 'the horizontal range "dista'ncefor the chosen airplaneground 'speed' and'horizontal triangle are introduced intothe've'rtical triangle CRG"*by varying the angle of the leveling bulb 30 with respect to the vertical line G"R representing theairplane altitudeyth'ereby altering the angle of elevation of sight to the target C"GR",'corresponding to CGR in Fig. 3, and altering the length of'the representative horizontal airplane-totarget 'distance line R"C".

Thus, by inserting into the present instrument the known data of the ground speed of the airplane, the altitude thereof, and the target aspect angle, and with the airplane on a collision course with the target 'as determined by the airplane pilot, the target may then be tracked withthe' bombsightand'theeXact point of release of the bombfor efiecting a hit on the target is indicated by means'of an optical system to be now described.

As described "above, the leveling bulb or spirit level 30 is a co rrelatingdevice properly uniting all the data inserted into the instrument to determine the angle of elevation or depression, these two angles being complimentary, for sighting onthe target when the range from theTai'rpla'ne to'the target is proper for release of the bomb to effect a hit on the target under the conditions of flight th'en existing. An electric lamp 5tl'is positioned above the. leveling bulb, and'the light therefrom is directed toward and transmitted through said bulb 30 by a suitable reflector (not shown), reflected upwardly by'right angle mirror 49 through collimating lens 51 to present an image ofthe bubble 53 Man infinite distance on transparent 'sigli't plate 52 'when*viewedalong the line of sight indicated in Fig. 5. In addition, the frame 31 for the leveling bulb has a relatively narrow slit 32 therethrough functioning as a fiducial line for the leveling bubble 53. The light from lamp 50 is also transmitted through slit 32 and reflected by mirror 49 upwardly through lens 51 to appear on sight plate 52 at an infinite distance when viewed along said line of sight. Although sight plate 52 is transparent so as to enable the bombardier to observe the target therethrough, it is sufficiently polished to partially reflect the images of the bubble 53 and the level fiducial line 32 so as to permit simultaneous observation of these images and the target. Thus, the several variables introduced into the device are correlated by the leveling bulb 31? and the result thereof is depicted by the bubble image on sight plate 52, to indicate the desired angle of depression of sight under the existing conditions of flight.

The optical system hereinabove described, comprising what is essentially a compound lens composed of the leveling bulb fluid and the bubble therein together with the collimating lens 51, would present a nonilluminated bubble image in an illuminated surrounding on the sight plate. This situation presents the obvious disadvantage of hindering target observation through the sight plate, particularly when target illumination is poor. However, by the provision of the diaphragm or light shielding strip 30a between the bulb 5t) and the level 39, which is made sufliciently wider than the image of the level and bubble formed by lens 51 on the sight plate, the image situation is reversed, the system yielding an illuminated bubble image in a nonilluminated surrounding on the sight plate, thus enchancing the observation of a target through the sight plate. The fiducial line appears at all times as an illuminated image. The diaphragm or light shielding strip 30a is slightly larger than and occupies the position of the image of lens 51 formed by the glass and liquid of the level 30 which may be considered as a cylindrical lens, assuming for the moment that the level 30 is completely filled with liquid. As will be readily apparent to those skilled in the art, no light can now pass from lamp or bulb 50 into the remainder of the optical system because of the presence of diaphragm 30a. Therefore, the bombardier, under these assumed conditions, observes a dark field. However, in the present invention there is a bubble in the level, and this bubble also acts as lens and collects deflected light which has passed around diaphragm 30a and which could not otherwise pass into lens 51. Therefore, an illuminated bubble image on a nonilluminated field is viewed on plate 52.

by the bombardier. This feature considerably enhances target observation as compared with observation available when the field is illuminated and the bubble not illuminated as would result if diaphragm 30a were not provided. It is desired to indicate that the focal length of the lens 51 is equal to the length of the optical path from the upper surface of the leveling bulb 30 to said lens, and that the leveling bulb 30 is formed with a lengthwise radius of curvature of its upper surface equal to the focal length of the lens 51, in order that the image of the bubble not be displaced in its optical distance from said lens when the entire instrument is tilted to various angles with horizontal, which is done during actual use of the bombsight as will be subsequently described.

In operation, therefore, when a collision course with the target has been determined and the attack run has begun, the airplane ground speed and altitude are in troduced into the instrument by means of the knurled dials and 25 respectively, and the target aspect angle is inserted into the instrument by sighting on the target through the sight plate 52 and adjusting the target aspect dial until arrow 16 points in the direction parallel to the targets course. The instrument is now set for tracking the target. This is accomplished by holding the instrument at such an angle as to bring the leveling bubble into coincidence with the fiducial line 32 as ob served by their images on the sight plate 52. With the; data thus inserted in the bombsight, it is apparent that registry of bubble 53 with fiducial line 32, whose angular position is determined by relative settings of ground speed, target aspect, and altitude, indicates that angle of depression of the line of sight to the target which is had when the airplane is at the proper bomb release point for obtaining a hit on the target, while the altitude determines the linear displacement of said image on the sight plate. Therefore, if the observer positions his eye on the line of sight, he may both-maintain the instrument at the proper angle of depression as indicated by the leveling bubble and fiducial marker images on the sight plate and simultaneously track the target through said sight plate.

The position of the registered leveling bubble image on the sight plate 52 is determined by the altitude setting inserted into the instrument, while the proper angle of depression for the line of sight to the target is determined by the ground speed and target aspect settings inserted into the instrument. As the plane approaches the point R where the bomb should be released, the registered bubble image'approaches coincidence with the target as sighted through the sight plate, as shown in Fig. 10, the approach, and Fig. 11, on target. If the leveling bubble is maintained coincident with the fiducial line 32 during the approach run, the bubble image comes into coincidenee with the target when theplane, flying the collision course established, reaches the proper range from the target as described above in the section General problems of bombing. By this device the bombardier can thereby determine the proper instant to release the bombs.

in the event that the target is stationary, the operation of the device is identical to that described for a moving target, except there being no target aspect angle, the target aspect arrow would point in a direction transverse to the line of sight through the sight plate 52, thereby eliminating the assumed target speed with respect to line of flight of the airplane, as set in by the distance from lug 24 to the center of pinion 22 and as depicted by the representative line OB, and the target is tracked in the same manner as described above.

Any of the above-described settings made on the present bombsight may be changed at any time that the conditions of flight or target course so alter as to make such changes necessary. For example, if the target should change course during the attack run, the pilot must alter the airplane heading to maintain a collision course, whereupon the bombardier must reset the target aspect angle accord-, ingly. Or if the airplane altitude and/or ground speed should be altered, commensurate changes in the respective settings must be made.

As mentioned above, the target speed is set into theinstrument by leg BC of the representative horizontal triangle. As described in the present disclosure, this distance is fixed and therefore effective only as against moving targets traveling at the rate represented thereby.

However, as will be readily apparent to those skilled in the art, any conventional means may be employed to alter the length of BC' proportionately to the speed of the target, thereby making the present bombsight effective and accurate against moving targets over a range of target speeds.

Submerged target The present invention also includes means for determining the proper point to release a bomb when a target such as a submarine submerges during the attack run. After the bombsight is set for a bombing run on a chosen target and the attack run has begun, in the case of a submarine target the submarine may submerge to elude the attack. The present bombsight is so constructed as to provide for accurate bombing in such an event by using the temporary swirl and oil slick left by the submarine when it submerges as the reference point upon which the bombsight is trained.

The functioning of this apparatus in this regard is basedbri the assumption that the submarine Continues itsmurse after "s'ubmerg'en'ce andthat' the pilot can prop erly alter his heading to maintain a'co'llision" course'therewith, and 'on -the further assumption' that 'the' 'submarine travelsat a known 'a'ndpredeter'mined"rate when 's'ubmerged. On the above mentio'ned"assumptions, a timing mechanism is-contained in the bombsight as apart of the present invention which, 'wh'en"desired," can be used'to' extend the'rateleg BC' of representative triangle C'BR', and in this way acorrection' factor is 'introduced"into the angular position of the leveling 'bulb enabling the" bombardier to train the sight on the temporary swirl or oil slick left by the submerged'craft and havethe proper range for release of the bomb referred'thereto in the manner described above, the movement of the target being'compensated for Within the instrument.

Referring to the horizontal analysis of Fig. 2, the airplane is flying the attack collision'course'AB' and a submarine is taking the course SB,"but"in this'i'nstance the submarine submerges at S after the above-described settings for the surfaced target have been inserted into the instrument. The bombardier uses the instrument as described above but keeps'the sight trained on the point of submergence S revealed by the oil slick or swirl left by the'submerged target, as indicated by the dotted line ES, while'the pilot must alter his course in order to maintain a collision course with the target. In this example it is assumed that the underwater speed of the submarine is the same as its'surface speed and that its underwater course is the same as its surface course, although the principles of operation involved are the same, in the present example the pilot does not alter his heading nor need any changes be made in the bombsight. Immediately on submergence of the target, then, the bombardier starts the timing mechanism which extends the rate leg BC to compensate for the travel of the submarine while he keeps the bombsight trained on the surface swirl or oil slick left by the submarine. If the timing mechanism operates in proportion to the underwater speed of the target, proper compensation is introduced in the position of the leveling bulb 30 so that the proper'moment for release of the bomb is indicated by coincidence of the bubble image with the surface swirl or oil slick on the sight plate '52, the proper range being depicted in Fig. 2 as line RS.

'As' described above for a surfaced target, R is the proper point for release of the bomb as indicated by the ra'n'ge'RC. But if the target submerges at S, the range RC "cannot be observed or determined, for there is no reference toindicate point C. However, if the underwater speed of the target is assumed to be known and an imaginary point D is caused to travel from C to S at the assumed rate at'which the target travels from S to C, then point D reaches S at the time that the target reaches C and the airplane reaches R, the proper point for release of the bomb. Therefore, if the travel of the imaginary point D is' inserted in the bombsight by causing the representative line BC' to be extended at a rate proportional to the assumed rate of travel of the submerged target, the necessary correction is introduced into the angular position of the leveling bulb in order that the range for release of the bomb may be referred to the swirl or oil slick left at S, the point of submergence, and the travel of the target is thus compensated. To this end the above-mentioned timing mechanism operates to so extend the representative line BC by moving the azimuth lug 24 as described in detail below. Thus, upon submergence of the target the pilotalters his heading-if necessary to maintain a collision course therewith, while the bombardier alters the target aspect angle if necessary, initiates the timing mechanism of the bombsight, and then keeps the sight trained on the swirl or oil slick left by the target at the point of submergence, otherwise using the instrument as described above for a surfaced target, The proper point for releaseof'the bomb is indicatedby coincidence of the leveledleveling bulbs bubble image'with the point of submergence.

The compensating device comprises a timing'motor 60 preferably of a spring windup type, although any other suitabletype of motor may be employed, gear 61 connected to one end of shaft 62a and pinion gear 22 connected to one end of shaft 62b and cooperating with azimuth rack 21 Shaft 62a is connected to shaft 62b through coupling 105, said coupling being so constructed as to enable the shaft 62a and its associated gear 61 to be moved into and out of engagement with the timer 60 along the axial line of the shaft without a corresponding movement of the shaft 62b and its associated pinion gear 22. In the tracking of a surface object the gear 61 is disengaged from timer 60 to enable free rotation of the target aspect dial 15 and permitting the rack 20 to be held in zero position by spring 64 as shown in Fig. 6. To efiectuate the timing compensatiornthe gear 61 is brought into engagement with timer 60 by any suitable means operated by lever 65, the movement also functioning to start the timer which is normally off. Operation of the timer 60 causes the pinion gear 22 to rotate at a predetermined rate thus moving the rack 20 at a predetermined rate, proportional to the target speed and effectuating the desired compensation by extending the line BC at the desired rate. As mentioned above, the timer is preset for a given underwater target velocity, but if desired, a rate control may be included in the timer for adjusting the same to various underwater target speeds.

The above description explains the operation of the present invention for bombing submerged targets when only the horizontal factors are considered. But it is apparent that the rate of change of the range RD as represented by RC is a function of the altitude of the airplane. It, therefore, is necessary that the rate of extension of representative line B'C' be made an equivalent function of the altitude. To this end the timer is provided with a timer cam stud 66 operated by cam slot 67, see Fig. 7, in the altitude dial 25. This stud and slot operate upon the timer to adjust its rate of operation in accordance with the altitude set into the device by the altitude dial, thereby controlling the rate of movement of azimuth rack 20 and the rate of extension of representative line BC', making the same a proper function of the airplane altitude.

The changes in line BC as effected by movement of rack 20 and its lug 24 are translated'into a corresponding alteration of the angular position of leveling bulb 30 by means of connecting chain 36, and thereby cause commensurate changes in the proper angle of depression of the line of sight as indicated through the optical system described above.

The-use of this device against submerged targets is intended to be applied only against such targets which have submerged after the attack run and the tracking of the target have been started while the target is surfaced. operation of the device is altered from the procedure discussed above for a surfaced target byimmediately on submergence altering the target aspect setting if necessary and moving lever 65 to operate timer 60 and to bring gear 61- and timer 60 into engagement, thereby putting the desired automatic compensation into representative triangle BC'R and thus into the angular position of leveling bulb 30. With this compensation thus introduced into the instrument for the assumed underwater speed of the target the bombardier then proceeds as described above under the discussion of surfaced target operation,except the sight plate is trained on the temporary swirl or oil slick at the point of submergence,

operation-is full described-above.

If during this attack the target submerges, the

As in the case of a surfaced target, the altitude and ground speed settings may be varied when necessary, but once the timer has been started the target aspect setting should not be altered.

Other features The present bombsight works in conjunction with a suitable electric control box receiving its current supply preferably from the airplane supply. This control box supplies the current for lamp 50 and has a suitable rheostat for controlling the brilliance of the light as desired by the bombardier for obtaining the optimum leveling bubble image.

In addition, the bomb release mechanism of the airplane is operated through said control box. The pistol grip handle 7 6 of the bombsight has a trigger 71 operating as the ultimate bomb release control. Before or during the attack the control box is set to operate the airplanes bomb release mechanism, but the activation of this control circuit is ultimately controlled by a switch in the handle 76 of the bombsight operated by the trigger 71. Thus, with the control box properly set, at the desired moment as indicated by the bombsight the bombardier presses trigger 71 thereby releasing the bomb, or a stick comprising a plurality of bombs.

When a stick or plurality of bombs is dropped, the pattern and position thereof which they form on reaching the ground is dependent on their relative positions in the stick of bombs before being dropped, the altitude of the airplane when dropped, and the air resistance and wind currents. The wind current is a negligible consideration in low altitude bombing and is ignored in the use of the present instrument. However, the other factors are not negligible and are compensated for in the present instrument so that the center of the ground pattern formed by the bombs corresponds to the center of the target when dropped at the proper range as determined by the instrument as aforedescribed.

The foregoing description of the present instrument considered the factors of bombing for an ideal or in vacuo trajectory of a single bomb. The present description considers the compensations necessary to correct for the trail of the bomb due to air resistance, for the situation where a stick of bombs is used to bring the center of the ground pattern formed thereby on the target, and, in the case of a submerged target, for the underwater travel of a bomb if a depth bomb is employed rather than an impact bomb. To accomplish these compensations, a plate 75, see Figs. and 9, is calibrated to compensate, when properly set, for the characteristics of the bomb stick used, the calibration being divided into fields of various altitudes, preferably for every 100 feet of altitude, and each altitude field is calibrated for various stick lengths, i. e. the length from one end to the other of the plurality of bombs comprising the stick, for the trail at each altitude field, and for the underwater travel of the bomb. A number of diflerently calibrated plates are employed, each plate 75 being calibratedin accordance with the appropriate characteristics of a particular type of bomb. The adjustment is then made by registering the proper reference line 76 of dial 77 with the proper calibration in the particular altitude field 110 of the calibrations in which the attack run is being made.

It is apparent that to lay the stick of bombs symmetrically across the target, the first bomb must be released at a point one half the stick length farther back along the line of flight than would be determined for a single bomb. The underwater travel of the bomb in the case of a depth bomb is accounted for by an additional backward displacement along the line of flight dependent upon the particular bomb characteristics. The small amount of trail is compensated for by a forward displacement along the line of flight and is also dependent upon the particular bomb characteristics. These various factors, then, may be added algebraically and imposed on the setting of the bombsight by introducing the proportionate correction in the line BR, representing the line of flight of the airplane. To this end, the ground speed dial 10 is provided with an inner differential dial 77 shown in cross section in Fig. 8. The dials l0 and '77 are independently rotatable through the annular friction bearing 112, while the relative rotation therebetween is limited to the extent of the various altitude fields by engagement of lugs 114, integral with dial 77, with stops 113, integral with dial 110, these lugs and stops being so positioned on their respective dials as to confine the relative movement therebetween to the extent of the various altitude fields. Thus, the desired compensation, as indicated by the calibrations on plates 75, may be introduced into the instrument by holding the dial 10 stationary while adjusting the dial 77, this adjustment being transmitted to the arm 12 and hence to the leveling bulb 30 by means of shaft and pinion gear 13 to the rack 14 on arm 12 in the same manner as the ground speed setting is inserted into the instrument. With the proper setting of dial 77 relative to dial 10, dial 10 may then be moved to introduce the proper ground speed, dial 77 then being left free to rotate with dial it as controlled by the friction bearing 112.

Fig. 9 is a detailed face view of the ground speed and the bomb characteristic dials. The lines denote the limits of each altitude field and hence the limit of movement of each reference line 76, each such line being confined to its field by the limit stops 113 and their associated lugs 114 described above. The calibrations 121 denote Zero stick length or represent the setting for a single bomb when it is desired to compensate for trail caused by air resistance and underwater travel of the bomb. The other calibrations denote the various stick lengths in feet as indicated. The distance between the ticular characteristics of the type of bomb being used,-

this being accomplished by having interchangeable plates 75 calibrated in accordance with the various types of The appropriate plate 75 is inserted on the velocity dial 10 and properly placed by registering posi tioning screw 78 with an opening therefor in plate 75'- bombs.

The plate is held in position by means of a snap ring or the like 79. Thus by removal of spring 79 the desired plate 75 may be properly inserted in the velocity dial "1 0 and the snap spring applied thereto to hold the plate in position. The reference line 76 for the appropriate altitude field is then positioned by means of knob 80 to cor respond with the desired calibration on plate 75. Rotation of knob 80 effects a rotation of gear 13 independent of dial 10 when dial 10 is held stationary, and thus through arm 12 introduces the desired correction into the representative horizontal triangle B'C'R'.

Conclusion t is therefore apparent from the foregoing description that the present device comprises a means for determining the range from a target at which a bomb should be dropped and for indicating when that range is reached. This is accomplished by a mechanism included in the bombsight for correlating the target aspect angle, the ground speed of the airplane, the altitude of the airplane, and various characteristics of the bomb or stick of bombs being dropped. The correlation is expressed by an angular and linear displacement of an indicator observed on the slight plate, so that when the sight line is held at the indicated angle of depression the indicator appears at various vertical displacements on the sight plate, thereby expressing the resultant range as a combination of the above data. The bomb release point is determined by coincidence of the indicator with the target as viewed through the sight plate. In addition, an automatic compensator is included in the instrument for continued tracking of a submarine after submergence thereof by using the temporary swirl or oil slick as the reference point for the bombsight and thereby determining the proper point for release of the bomb.

The above detailed description of one embodiment of the present invention is presented merely by way of example, and the scope of the invention is not limited thereto. Modifications within the spirit and scope of the present invention as defined by the appended claims will be apparent to those skilled in the art, and are therefore within the contemplation of the present patent.

What is claimed is:

1. In a bombsight having a spirit level for correlating airplane speed, airplane altitude, and target aspect to indicate by rotational and linear movement thereof the proper bomb release position relative to a target for obtaining 21 hit thereon; an optical system comprising a movably mounted frame member having a slitted portion defining a fiducial line, said spirit level mounted on saidframe member inwardly from the edges thereof, a light source mounted above the level directed downwardly toward the level, a right angle mirror mounted below the level for transmitting an image of the bubble in the level and the fiducial line, a collimating lens positioned above said mirror and in the optical path of light transmitted through said level and via said mirror for transmitting an image of the levels bubble, a semirefiective sighting plate positioned in the optical path of said transmitted image, and a light shielding strip completely opaque throughout the length and width thereof and interposed between said light source and said level for completely shielding from direct light the portion of the level optically corresponding to the area of the sighting plate, said light shielding strip extending the full length of said level and directly connected at each end to said frame'member inwardly from the edges thereof to provide a path for direct light from the light source to the slitted portion of the frame member and the remainder of the frame member laterally of the level and thence a path for indirect light deflected by said frame member into said level and level bubble, leveling of said spirit level thereby'providing a reference image on said plate and registry thereof with the target as obtained by sighting throughsaid plate indicating the bomb release position.

'2. In a bombsight having-a fluid levelingbulb having a free floating bubble for correlating pertinent airplane and target data to indicate by movement thereof the proper bomb release position relative to atarget for obtaining a hit thereon; an optical system comprising" a movably mounted frame member having a' slitted portion defining a fiducial line, said leveling bulb mounted on said frame member inwardly from the edges thereof, a light source directed downwardly toward the bulb, a completely opaque light shielding strip interposedbetween said light source and said bulb for shielding said bulb from direct light from the light source, said light shielding strip extending the full length of said bulb and connected at each end to said frame'member inwardly from the edges thereof to provide a path fordirect light from said light source to the slitted portion of the framememberand the remainder of the frame member laterally of said bulb and thence a path for indirect light deflected by said frame member into said bulb and bubble, a right angle mirror disposed below said bulb for transmitting an image'of the bubble and the fiducial line, a collimating lens positioned above said mirror and in the optical path of light transmitted through said bulb and via 'said mirror, and a sighting plate positioned above said collimating lelnsarid in the optical path of said transmitted image, said light Iii; shielding strip providing an illuminated image of the bubble in a nonilluminated surrounding on said plate, leveling of said bulb thereby providing a reference image on said plate and registry of said image with the target as obtained by sighting through said plate indicating the bomb release position.

3."An optical sighting system comprising a movably mounted frame member having a slitted portion to function as a fiducial line, a light source mounted above said frame member and directed downwardly toward the latter, a spirit level mounted on said frame member inwardly from the edges thereof, a right angle mirror disposed below said spirit level for transmitting an image originating in said spirit level, a collimating lens positioned above said mirror and in the optical path of light transmitted through said level and via said mirror for transmitting an image of the levels bubble, a semireflective sighting plate positioned in the optical path of said transmitted image enabling a correlation of the image position on said plate with an object by sighting therethrough, and a light shielding strip completely opaque throughout the length and width thereof and interposed between said light source and said level for completelyfshielding the level from direct light, said light shielding strip extending the full length of said level and directly connected at each end to said frame member inwardly from the edges thereof to provide a path for direct light from the light source to the slitted'portion of the frame member and the remainder of the frame member laterally of the level and thence a path for indirect light, deflected by said frame member into said level and level bubble, the system thereby providing an illuminated image of the bubble in a nonilluminated surrounding on said plate.

4. An optica] sighting system comprising a movably mountedframe member having a slitted portion defining a fiducial line, a light source mounted above said frame member and directed downwardly toward the latter, a fluid leveling bulb having a free floating bubble and mounted on said frame member inwardly from the edges thereof and for movement therewith, a completely opaque light shielding strip interposed between said light source and said bulb for shielding said bulb from direct light from said light source, said light shielding strip extending the full length of said bulb and directly connected at each end to said frame member inwardly from the edges thereof to provide a path for direct light from the light source to the slitted portion of the frame member and the remainder of the frame member laterally of the bulb and thence a path for indirect light deflected by said frame member into said bulb and bulb bubble, a right angle mirror disposed below said bulb for transmitting an image of the bubble and fiducial line, a collimating lens positioned above said mirror and in the optical path of light transmitted via said bubble and mirror for transmitting an image of the bubble, and a sighting plate positioned above said collimating lens and in the optical path of said transmitted image enabling a correlation of the image position on said plate with an object by sighting therethrough, said light shielding strip being larger than the image on the collimatinglens formed by the leveling bulb thereby providing an illuminated image of the bubble in a nonilluminated surrounding on said plate.

References Cited in the file of this patent UNITED STATES PATENTS 1,063,761 Aldis June 3, 1913 2,352,644 Lindarman et al. July 4, 1944 2,404,746 Rylsky et al. July 23, 1946 2,412,585 i ilemperer et al. Dec. 17, 1946 2,464,195 Burley Mar. 8, 1949 2,566,389 Walk Sept. 4, 1951 

